81 has the square root of 9.
Square root of 3= 1.73205080757
Square root of 4= 2.02484567313
Square root of 18= 4.24264068712
It depends on how many groups one thing that helps is if you draw circle as the group and add one tally to each of them till you hit 24 then you habe your answer
Check the picture below.
so the volume will simply be the area of the hexagonal face times the height.
The answer for that problem is z =12+6